Swfdec is a project to write a Free Flash player. It contains of a player library libswfdec and various applications making use of it. One of those is the Swfdec mozilla plugin, that plays back Flash content in supporting browsers. However, there is multiple advantages with integrating Swfdec natively into Webkit: - No overhead and limitations when using the NPAPI. (This is a maintenance problem, not a performance issue) - Can make use of various backends directly. Examples include Cairo (+ printing), Accessibility, GStreamer and libsoup. - Tighter integration with the browser's features. Examples here include sharing of settings (cookies, audio/video, popups, autoplay etc), shared caching, including requested files in the page info or providing a proper right-click menu. - And last but not least, it's simple to swap in other Flash plugins on-demand for specific sites should the user wish to do that.
Since swfdec development seems to be discontinued I guess we can close this for now (maybe open another bug for Gnash).